The present invention relates to an image processing technique to improve image quality of an image generated by an image pickup apparatus such as a digital camera.
An optical image formed by a refractive optical system such as a lens includes aberrations, and it is important to suppress the aberrations in optical design of the refractive optical system. In particular in recent years, an image sensor (image pickup element) has a high resolution, and a user often enlarges an image obtained by an image pickup apparatus when watching the image, which makes even a small aberration noticeable.
Methods for suppressing the aberrations include a method combining concave and convex lenses having different refractive indexes and different curvatures and a method using an optical element having special optical characteristics such an optical element formed of fluorite, or a DOE (diffractive optical element). However, aberration correction by such optical methods increases cost and weight of the image pickup apparatus, which goes against requirement of miniaturization and lightening of the image pickup apparatus.
Therefore, it is desired to perform aberration correction by image processing. An aberration correction method using image processing is disclosed in, for example, Japanese Patent Laid-Open No. 2000-003437. The aberration correction method disclosed in Japanese Patent Laid-Open No. 2000-003437 first corrects distortion of digital image data constituted by brightness data and color difference data, and then converts the brightness data and the color difference data into RGB data to correct chromatic aberration of magnification.
The aberration correction method disclosed in Japanese Patent Laid-Open No. 2000-003437 can correct the distortion and the chromatic aberration of magnification. However, this aberration correction method cannot correct chromatic aberrations other than the chromatic aberration of magnification.
In order to obtain digital image data having a higher image quality, a more highly precise correction of chromatic aberrations, that is, correction of chromatic aberrations including longitudinal chromatic aberration is required.